In recent years, it has become apparent that organic semiconductor materials possess superior electrical properties in comparison with inorganic semiconductor materials, and progress has been made in the development of applications to various electronic device fields. An organic thin film transistor (TFT), which utilizes an organic semiconductor film in a semiconductor channel, is easier to process than an inorganic semiconductor and permit application of simple and inexpensive manufacturing processes. In addition, by permitting fabrication in the vicinity of room temperature, they enable semiconductor technologies based on the use of plastic substrates and are expected to be used as post-silicon semiconductors.
Depending on the characteristics of the materials, various methods, such as vapor deposition processes, molecular beam epitaxy solvent evaporation processes, melt processes, the Langmuir-Blodgett process, and the like, heretofore have been investigated as methods for fabricating a crystalline organic semiconductor thin film for use in organic TFT.
An example of an improved method, in which an organic single crystal film is fabricated by a solvent evaporation process, is disclosed in Patent Document 1. This method is an improvement over the conventional method, in which multiple substrates of quartz and the like were stacked, and organic single crystal films were grown between these substrates with the help of a solvent evaporation process. Specifically, it changes the approach, in which substrates are placed in a vessel containing a solution of an organic substance horizontally with respect to the surface of the solution, and involves conducting the solvent evaporation process while keeping the substrates inclined with respect to the surface of the solution. This is aimed at accelerating the process of solvent evaporation up to the range required for crystal growth between the substrates in order to improve seed crystal generation and the efficiency of the growth process.
Among the methods based on the principle of solvent evaporation, solution processes utilizing solutions, such as droplet formation, spin-coating, and printing, are the most desirable methods for the development of high-performance organic TFTs due to their simplicity and the fact that they are inexpensive and permit fabrication in the vicinity of room temperature. The solution process is a method in which dripping or applying an organic semiconductor material solution to the surface of a substrate and drying the solvent contained in the droplets brings the solution into a saturated state via solvent evaporation and causes crystals to precipitate, thereby forming an organic semiconductor thin film.